Thanks everyone for the interesting points raised.

I'd like to add that while the SSXL (4.5 or otherwise) has aspherical elements which likely reduced the number of spherical elements needed for comparable correction, still the difference between 78° and 105° is huge and would have needed more elements anyway. So the SSXL having I don't quite agree that the SSXL having an explicitly stated recommended working aperture of f/16 (or is it f/22?) means that the Fuji lens here is optimised to be shot wide open at f/4.5. Also it's not very clear that the Fuji lens is retrofocus because as I said, it sits a decent way away from the film plane although the proportions of the camera makes things look like the lens is very close to the film.

So my conclusion is... it's difficult to draw a lot of insight from existing lenses without making apple-to-orange comparisons. And with lens designs being so closely related it's sometimes not easy to make distinctions.

Dan: I was asking about any lens, not just this lens.

Thanks again for all the inputs... would also be interesting to hear thoughts from anyone who has designed lenses on a ray tracer.

G